1. Field of the Invention
This invention relates to toner cartridges used in electronic or laser printers and more particularly to the sensors and timing mechanisms on the cartridge for controlling printer operation and status.
2. Background Information
Electronic or “laser” printers use a focused light beam to expose discrete portions of an image transfer drum so that these portions attract printing toner. Toner is a mixture of pigment (typically carbon black or a non-black color component) and plastic. The toner becomes electrostatically attracted to exposed portions of the image transferred drum. As a transfer medium such as paper is passed over the rotating image transferred drum, some of the toner is laid onto the medium. Subsequently, the medium passes through a heated fuser so that the plastic is melted into permanent engagement with the underlying medium.
The vast majority of desktop laser printers currently available utilize replaceable toner cartridges that incorporate an image transfer drum, a toner tank and a metering system and a drive mechanism for the drum and metering system. Modern toner cartridges often include a variety of sensors that interact with the laser printer in order to indicate the status of the cartridge. Indications relating to toner level, print quality and general cartridge function are often included. A large number of types and sizes of toner cartridges are currently available. Each cartridge is provided with its own set of operating parameters and toner fill limitations. Certain cartridges, such as those used in the E320/E322™ series printer, available from Lexmark® utilize a complex sensing system for determining cartridge performance. It should be noted that the principles discussed herein apply generally to any toner cartridge that employs a spring-loaded decoder or timing mechanism to track toner level and associated functions.
The cartridge's sensing system includes an encoder or timing wheel interconnected with one end of a rotating agitator blade within a cylindrical toner tank. Movement of the agitator blade feeds toner into the metering system. The timing wheel reports the movement of the agitator wheel through the toner reservoir. The resulting signal must fall within certain perimeters, or a variety of error conditions are indicated by the printer, and print engine operation may suddenly cease.
The timing wheel includes a set of perimeter notches at predetermined arcuate positions. The notches interact with an optical or electromechanical sensor on the print engine. The timing wheel is fixed to the agitator blade via a common shaft. Coaxially mounted on the shaft is a main drive gear that is operatively connected with the print engine drive train. The timing wheel and agitator blade shaft together provide “lost motion” or dwell (or “float”) with respect to the drive gear within a predetermined arcuate limit. This limit is set by two opposing stops formed on an arcuate slot of the timing wheel. This arcuate slot rides on a stop post that extends from the drive gear. In general the motor rotates the drive gear through a full rotation to bring the agitator from a position above the toner, through the toner, and back out again. However, the float or dwell of the drive gear relative to the timing wheel causes a degree of play in the characteristic rotation between the drive gear and the timing wheel/agitator assembly.
To control the level of lost motion/dwell, the timing wheel is operatively connected to a spring that engages a post on the drive gear. When the drive gear is rotated by the motor, the timing wheel (and hence, the shaft of the agitator blade) is normally biased against the first of the two stops through back pressure exerted by the spring against the timing wheel. Any resistance on the agitator blade—caused generally by contact with toner—induces resistance to rotation and causes the timing wheel to begin to lag the rotation of the drive gear (with the spring being loaded and beginning to elastically deform, thereby causing the timing wheel's first stop to rotate away from the drive gear's stop post). If the resistance is strong enough, the timing wheel will strike the drive gear's stop post with its second, opposing stop (having rotated through the full arcuate dwell range), the spring being fully loaded at this point.
Naturally, if the spring is loaded by resistance as the agitator blade drags through the toner, eventually the agitator blade reaches a point near top of the toner supply and the resistance is overcome—often abruptly. At this point, the timing wheel's spring tends to rotationally snap the agitator arm upwardly out of the remaining toner supply, thereby relieving some of the spring force and bringing the timing wheel against the first drive gear stop again. The drive gear moves through each 360-degree cycle at a substantially constant rate of rotation. However, it should be clear that the dwell causes the timing wheel to display a variable rotational rate throughout its own associated 360-degree cycle. The variation in this rate causes the notches in the perimeter to be presented to the sensor at certain times that are compared to the constant timing of the motor. By determining whether these notches appear at the appropriate time in the cycle, the print engine can determine several parameters. For example, little movement of the first stop by the timing wheel indicates little resistance, and hence a low-toner supply. Likewise, little snapback confirms low toner. Conversely, a large rotational movement occurring early in the in the cycle, followed by a late and significant snapback may indicate an overfilled cartridge. Both these conditions cause the print engine's logic to signal an appropriate problem and (possibly) disable further print operations.
The strict limits placed upon this cartridge, and others, can prove difficult to overcome for manufacturers seeking to provide a higher-capacity toner tank for compatible cartridges. This is because manufactured and remanufactured cartridges must include no more than the original manufacture (OEM) toner level even if a higher level can be provided with appropriate performance. A higher level causes the agitator blade to move differently through the reservoir, thereby sending the above-described error/problem signal to the printer.
Commonly owned U.S. Pat. No. 6,510,303 B2, entitled EXTENDED-LIFE TONER CARTRIDGE FOR A LASER PRINTER, by Lionel C. Bessette, the teachings of which are expressly incorporated herein by reference, addresses certain problems encountered in providing a higher initial toner charge to a cartridge with strict sensing limitations on volume. A main improvement is the repositioning of timing slots on the timing wheel so that they trigger appropriate status signals for overfilled operation. Another improvement described in that patent entails the use of a spacer on a stop post that limits the range of dwell of the drive gear with respect to the agitator by reducing the spacing of the post from the first stop and the second stop. This modifies the snapback properties of the agitator and so that the timing of snapback is appropriate for higher-than-specified toner levels.
Likewise, to effect proper timing in an “overfilled” condition, the spring that provides resistance between the drive gear and agitator may be replaced with one having a higher spring force than the OEM-version spring. This would effectively allow snapback to occur earlier (at a time specified for an OEM-toner level) as the agitator can now drag itself through, and out of, the thicker (overfilled) layer of toner. However, a stronger replacement spring may provide little or no resistance-based dwell off of the first stop at a low (but not empty) toner condition. This may trigger the print engine to enter a “low-toner” condition prematurely, wasting toner and defeating the purpose of an extended-life cartridge. A more-comprehensive and elegant system for dealing with the great variation between overfilled conditions and minimal toner conditions is needed to apply to a broader range of cartridges.